Synthetic Populations – Sources of Precocity in Maize Breeding
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Research Journal of Agricultural Science, 44 (2), 2012 SYNTHETIC POPULATIONS – SOURCES OF PRECOCITY IN MAIZE BREEDING I. HAS1,2, Voichiţa HAS2, A. GULEA3 1University of Agricultural Sciences and Veterinary Medicine Cluj-Napoca 3-5 Mănăştur Street, Postcode 400372, Cluj-Napoca, Romania 2 Agricultural Research and Development Station Turda 3Cattle Research and Development Station, Targu-Mures, Romania E-mail: [email protected] Abstract: In the maize breeding the local landraces precocity, such as: Avram Iancu, Bereni, Corbu could presented a special interest, evenly like 189-84, Cerbal, Dumbravita, Desesti, Mara1, useful gene sources for adapting capacity and for Mara2, Eremitu, Giulesti, Satu Lung, Satu Mare, physiological and agronomical traits and for Tarna Mare, Vlaha, and synthetic populations Tu valuable quality. The exploration of these Syn. 6, Tu Syn Mara1, Tu Syn Gutin, Tu SRR resources can be possible only through complexes 2I(5D), Myn Syn AS-G. The determination of the studies and measures which will determine the genetic value of seven synthetic consisted in their biodiversity keeping and the sustainable use of this. crossing with four testers (inbred lines): two flint The creation of maize hybrids which, among other inbred lines (TD 233 and CO 255) and two dent features, to be early it is a big concern of breeder inbred lines (TC 184 and TC 209). The test crosses teams. In northern and pre-montane areas, due to and their parental forms were evaluated in four thermal lowered resources, precocity is environmental conditions: two years 2009 and indispensable to achieving maturity. The objectives 2010 and two locations Turda and Targu-Mures of this research were: -to explore the phenotypic respectively, for both per se and test cross variability existing for early maturity in a large performances. The highest values of additive effects range of maize local and synthetic populations; -to for grain dry matter content were recorded at: Tu identify genotypes that could be interesting in Syn Mara (ĝn = +1.80), Tu SRR 5D (2I) (1) (ĝn = heritability of short growing season. It was noticed +0.62) and Tu Syn 1 (ĝn = +0.45). Therefore, Tu some maize local populations which can be used Syn Mara, Tu SRR 5D (2I)(1) and Tu Syn 1 like initial genetic material for breeding of produced hybrids with the most early maturity. Key words: maize germplasm, precocity, GCA, general combining ability; SCA, specific combining ability INTRODUCION The maturity ratings of maize (Zea mays L.) varieties usually grown in Transilvania (central and north-western Romania) rang from FAO 100 to 400. Late material normally shows too much moisture at normal harvesting time and then presents problems with storage. This severely limits the scope of the germplasm that can be used in a breeding program located in this area. Selection for early flowering and low moisture at harvest adapts later material to areas that require earlier maize (GIESBRECHT, 1960; ORDAS, 1988; HAWBAKER et al., 1996; GONZALEZ et al., 1997; TROYER, 2001; TALLER and BERNARDO, 2004; SHRANG et al., 2006) Choosing reliable maize varieties that are early maturing is essential for maize growers in the areas with limited heat treatment, but that doesn’t mean losing out on yield. These genotypes, in effect, require a shorter growing season than later maturing ones. Flint x dent maize hybrids are commonly planted in the early corn growing regions of Europe (northern and the Atlantic Coast of Europe). Evaluation of the early maize germplasm is important for the development of new commercial hybrids adapted to cooler summer regions (REVILLA et al., 1999; GONZALEZ et al., 2000). Local populations to improve maize may be of particular interest, especially as gene 33 Research Journal of Agricultural Science, 44 (2), 2012 sources for resilience and some agronomic properties (MURARIU et al., 2010). The most valuable populations have undergone extensive works of inbreding and selection for the creation of inbred lines, hybrids that provide it with a better language capacity to adapt in comparison with foreign hybrids. Partial results confirmed expectations (SARCA, 2004). Local populations of maize are distinguished by a great capacity of adaptability and physiological properties specific to certain areas, and a production capacity and outstanding quality. Each population bears the imprint of the environment in which it was formed (TROYER, 2001). Romanian local populations are very different, as are the environmental conditions in our country. Local populations are the result of a long process of evolution, under the action of factors that determine evolution, possessing assets particularly valuable that the inbred lines can transfer these traits of hybrids, which highlight the poignancy of appropriating adaptability (CRISTEA, 1978). Development of such hybrids is fully possible, whereas in local populations of corn in our country there are genetic factors responsible for the manifestation of these assets. For efficient use of local germoplasm, it must be inventoried and stored valuable genes. Characterizing maize genetic resources and understanding the structure of the diversity they encompass should lead to enhanced utilization for the improvement of this crop. Vegetative traits can be included as descriptors for describing and characterizing maize germplasm (ORTIZ et al., 2008; ORTIZ et al., 2009). The obtaining of maize hybrids which, among other features, to be early too, represents an important concern of the maize breeders. Early maize must grow faster and mature sooner under cooler conditions than later maize, to produce mature kernel in a shorter season. Early maize grows faster, particularly in the spring when the weather is cool. European northern flint varieties, as sources of early germplasm, grow extremely fast in seedling and in juvenile plant stages, flowers sooner and reaches physiological maturity sooner than later maize (HAS, 2001). Maturity zones are based on accumulated GDUs during the frost-free period: GDU = [Max temp (≤ 300C) + Min temp (≥ 100C)]/2 - 100C. In northern and premontane areas, due to limited thermal resources, precocity is indispensable to achieving maturity (CRISTEA et al., 1986, 1986a; CABULEA, 1987). In southern areas, precocity is used to mitigate the moisture stress of late drought by sowing earlier and early use of earlier hybrids (CIOCAZANU et al., 1998; BAGIU, 1999). Some of sources of early germplasm might be local and synthetic populations breeding by recurrent selection (CRISTEA et al, 1978; GULEA, 2011; HAS et al., 2011). The inheritance of maturity in maize is governed quantitatively. In general, the genes act in an additive manner, as if many genes with small and equal effects were involved; heterosis affects flowering time about 10% (TROYER, 1994, 2001). Knowledge about germplasm diversity and genetic relationships among breeding materials could be an invaluable aid in maize improvement strategies, maize germplasm could be easily managed, using recurrent selection method (LAVERGE et al., 1991; MOHAMMADI and PRASANNA, 2003; TALLER and BERNARDO, 2004). Turda - Romania maize genotypes have great phenotypic and genetic variability, consisting of local populations, varieties, synthetics. Genotype germplasm sources range from very early to lateand from dent to flint grain characteristics (HAS et al., 2006). The objectives of this research were: -to explore the phenotypic variability existing for early maturity in a large range of maize local and synthetic populations; -to identify genotypes that could be interesting in heritability of short growing season. 34 Research Journal of Agricultural Science, 44 (2), 2012 MATERIALS AND METHODS Maize samples I. Phenotypic variability Maize samples used in this study consisted of 264 accessions from “TURDA” germplasm collection, among which there were 208 local populations (landraces), collected in different Romanian regions (Transylvania and Moldavia); 56 synthetics/composites among which 30 synthetics created at ARDS Turda and 26 synthetics acquired from different countries (Spain, Italy, Germany, University of Minnesota, University of Pennsylvania). All local populations (landraces) and synthetics are currently used in the framework of breeding and genetic program at the Agricultural Research Station, Turda – Romania (ARS Turda). The studied genotypes differed by germplasm source, grain type, maturity classification (very early, early, intermediate and late) and grain appearance and colour. Experimental designs. These genotypes were grown at the Agricultural Research and Development Station Turda – Romania (Transylvania region), in 2009. Each group of genotypes was grown in separate but adjacent trials. Experimental plots were 2-rows, 5 m - long, with 0.7 m spacing between two rows without replications. Plant densities averaged 60 000 plants/hectare in each trial. I.Statistical analysis of per se variability. All stages of growing season were performed in duplicate, and the mean value was analyzed statistically. Analyses of variance (ANOVA) using a one-factor model without replications were done for each trait and for each group of genotypes (CEAPOIU, 1968). Standard deviation: Coefficient of variation (CV %): II. Genotypic variability Seven early maturing maize synthetic populations derived from three different breeding programs were chosen for this study: 1) per se selection (Tu Syn 3 (per se) (1)), 2) recurrent selection (Tu Syn Mara, Tu Syn 1, Tu Syn 8), 3) recurrent reciprocal selection (Tu SRR 2I(5D) (1),